Non-volatile memory cells employing a transition metal oxide layer as a data storage material layer and methods of manufacturing the same

ABSTRACT

Non-volatile memory cells employing a transition metal oxide layer as a data storage material layer are provided. The non-volatile memory cells include a lower and upper electrodes overlapped with each other. A transition metal oxide layer pattern is provided between the lower and upper electrodes. The transition metal oxide layer pattern is represented by a chemical formula M x O y . In the chemical formula, the characters “M”, “O”, “x” and “y” indicate transition metal, oxygen, a transitional metal composition and an oxygen composition, respectively. The transition metal oxide layer pattern has excessive transition metal content in comparison to a stabilized transition metal oxide layer pattern. Methods of fabricating the non-volatile memory cells are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of Korean Patent Application No.2004-72754, filed Sep. 10, 2004, the disclosure of which is herebyincorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices and methods ofmanufacturing the same and, more particularly, to non-volatile memorydevices and methods of manufacturing non-volatile memory devices.

BACKGROUND OF THE INVENTION

Non-volatile memory devices retain their stored data even when theirpower supplies are turned off. Therefore, non-volatile memory deviceshave been widely used in computers, mobile telecommunication systems,memory cards and so on. Flash memory devices are widely used asnon-volatile memory devices. Many flash memory devices employ memorycells having a stacked gate structure. The stacked gate structureincludes a tunnel oxide layer, a floating gate, an inter-gate dielectriclayer and a control gate electrode, which are sequentially stacked on achannel region. Film quality of the tunnel oxide layer should beimproved in order to improve reliability and program efficiency of theflash memory cells, and a coupling ratio of the flash memory cell shouldbe increased.

Recently, novel non-volatile memory devices, for example, resistancerandom access memory (RAM) devices have been proposed instead of flashmemory devices. A unit cell of a resistance RAM device includes a datastorage element having two electrodes and a variable resistive materiallayer interposed between the two electrodes. The variable resistivematerial layer, that is, a data storage material layer, may be changedinto a conductor or an insulator according to a polarity and/or amagnitude of an electrical signal (voltage or current) applied to theelectrodes. In other words, the data storage material layer has aswitchable state. The voltage required to convert the data storagematerial layer to the insulator is referred to as a reset voltage, andthe voltage required to convert the data storage material layer to theconductor is referred to as a set voltage.

Resistance RAM devices are disclosed in U.S. patent Publication Nos. US2003/00011789 A1, US 2003/0148545 A1 and US 2003/0003674 A1 as well asU.S. Pat. No. 6,583,003 B1. According to these conventional devices, apraseodymium calcium manganese oxide (Pr,Ca)MnO₃) layer (hereinafter,referred to as a “PCMO” layer) is used as the data storage materiallayer. However, it is difficult to pattern the PCMO layer using aconventional photolithography/etch process, which is widely used in thefabrication of semiconductor devices. This patterning complexity maylead to difficulties in improvement of integration density of resistanceRAM devices employing a PCMO layer. In addition, four kinds of materialsshould be mixed to form the PCMO layer. Thus, it may be difficult toform the PCMO layer having a uniform composition throughout thesemiconductor substrate. Moreover, a ZnO-based data storage materiallayer is disclosed in U.S. Pat. No. 4,472,296 to Hunter, Jr. et al.According to Hunter, Jr. et al., the ZnO-based data storage materiallayer has a switching characteristic at a high voltage of about 50 V.

SUMMARY OF THE INVENTION

According to aspects of the present invention, there are providednon-volatile memory cells having a transition metal oxide layer. Thenon-volatile memory cells comprise an insulating layer formed on asemiconductor substrate and lower and upper electrodes formed on theinsulating layer. The lower and upper electrodes overlap with eachother. A transition metal oxide layer pattern is interposed between thelower and upper electrodes. The transition metal oxide layer pattern isexpressed by a chemical formula M_(x)O_(y). In the chemical formula, thecharacters “M”, “O”, “x”, and “y” indicate transition metal, oxygen, atransitional metal composition and an oxygen composition, respectively.The transition metal oxide layer pattern contains excessive transitionmetal in comparison to a stabilized transition metal oxide layerpattern. In some embodiments, when the transition metal “M” is one ofnickel (Ni), cobalt (Co), zinc (Zn) and copper (Cu) and the transitionmetal composition “x” is 1, the oxygen composition “y” may be within arange of 0.5 to 0.99. In other embodiments, when the transition metal“M” is one of hafnium (Hf), zirconium (Zr), titanium (Ti) and chromium(Cr) and the transition metal composition “x” is 1, the oxygencomposition “y” may be within a range of 1.0 to 1.98. In yet otherembodiments, when the transition metal “M” is iron (Fe) and thetransition metal composition “x” is 2, the oxygen composition “y” may bewithin a range of 1.5 to 2.97. In still other embodiments, when thetransition metal “M” is niobium (Nb) and the transition metalcomposition “x” is 2, the oxygen composition “y” may be within a rangeof 2.5 to 4.95.

In yet still other embodiments, the lower electrode may be an iridium(Ir) layer, a platinum (Pt) layer, an iridium oxide (IrO) layer, atitanium nitride (TiN) layer, a titanium aluminum nitride (TiAlN) layer,a ruthenium (Ru) layer, a ruthenium oxide (RuO) layer or a polysiliconlayer. In further embodiments, the upper electrode may be an iridium(Ir) layer, a platinum (Pt) layer, an iridium oxide (IrO) layer, atitanium nitride (TiN) layer, a titanium aluminum nitride (TiAlN) layer,a ruthenium (Ru) layer, a ruthenium oxide (RuO) layer or a polysiliconlayer.

The lower electrode may be electrically connected to the semiconductorsubstrate through a contact plug that penetrates the insulating layer. Abuffer layer may be interposed between the lower electrode and theinsulating layer. The buffer layer extends to cover the contact plug.The buffer layer may be a single buffer layer. Alternatively, the bufferlayer may comprise a lower buffer layer and an upper buffer layer whichare sequentially stacked.

An inter-metal dielectric layer may also be provided on the substratehaving the lower electrode, the transition metal oxide layer pattern andthe upper electrode, and a bit line may be provided on the inter-metaldielectric layer. The bit line is electrically connected to the upperelectrode. The lower electrode, the transition metal oxide layer patternand the upper electrode may be covered with a capping layer, and aninter-metal dielectric layer may be provided on the substrate having thecapping layer. The upper electrode is electrically connected to a bitline disposed on the inter-metal dielectric layer. The capping layer maybe an aluminum oxide (AlO) layer.

In additional embodiments, an access transistor may be provided at thesemiconductor substrate. The access transistor may include source/drainregions formed in the semiconductor substrate and a gate electrodedisposed to cross over a channel region between the source/drainregions. The drain region is electrically connected to the lowerelectrode.

According to other embodiments of the present invention, methods ofmanufacturing a non-volatile memory cell having a transition metal oxidelayer are provided. The methods include forming an insulating layer on asemiconductor substrate and forming a lower electrode layer on theinsulating layer. A transition metal oxide layer is formed on the lowerelectrode layer. The transition metal oxide layer is represented by achemical formula M_(x)O_(y). In the chemical formula, the characters“M”, “O”. “x” and “y” indicate transition metal, oxygen, a transitionalmetal composition and an oxygen composition, respectively. Thetransition metal oxide layer is formed to contain excessive transitionmetal in comparison to a stable transition metal oxide layer. An upperelectrode layer is formed on the transition metal oxide layer. The upperelectrode layer, the transition metal oxide layer and the lowerelectrode layer are patterned to form a lower electrode, a transitionmetal oxide layer pattern and an upper electrode which are sequentiallystacked.

In some of these embodiments, the transition metal oxide layer may beformed by alternately and repeatedly performing a process for forming atransition metal layer and a process for oxidizing the transition metallayer using an oxygen plasma treatment technique. Alternatively, thetransition metal oxide layer may be formed using a sputtering technique.In addition, the oxygen plasma treatment may be performed using anin-situ process. In other embodiments, the transition metal oxide layermay be formed using an O₂ reactive sputtering technique, a chemicalvapor deposition technique or an atomic layer deposition technique.

In still further embodiments of the invention, an access transistor maybe formed at the semiconductor substrate prior to formation of theinsulating layer, and a contact plug may be formed in the insulatinglayer. The access transistor may be formed to have source/drain regionsformed in the semiconductor substrate and a gate electrode disposed tocross over a channel region between the source/drain regions, and thecontact plug may be formed to electrically connect the lower electrodeto the drain region. In addition, a buffer layer may be formed to coverthe insulating layer and the contact plug prior to formation of thelower electrode layer. The buffer layer may be additionally patternedafter formation of the lower electrode. The buffer layer may be formedof a single buffer layer. Alternatively, the buffer layer may be formedby sequentially stacking a lower buffer layer and an upper buffer layer.

In still further embodiments, an inter-metal dielectric layer may beformed on the substrate having the lower electrode, the transition metaloxide layer pattern and the upper electrode, and a bit line may beformed on the inter-metal dielectric layer. The bit line is electricallyconnected to the upper electrode. Prior to formation of the inter-metaldielectric layer, a capping layer may be formed to cover the lowerelectrode, the transition metal oxide layer pattern and the upperelectrode. The capping layer may be formed of an aluminum oxide (AlO)layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view illustrating resistance RAM cellsaccording to embodiments of the present invention;

FIGS. 2 to 4 are cross-sectional views that illustrate methods ofmanufacturing the resistance RAM cells shown in FIG. 1;

FIG. 5 is a flowchart to illustrate methods of forming a transitionmetal oxide layer of a resistance RAM cell according to embodiments ofthe present invention;

FIG. 6 is a graph illustrating x-ray photoelectron spectroscopy (XPS)data of nickel oxide layers formed according to embodiments of thepresent invention;

FIG. 7 is a graph illustrating resistivity and forming voltage of nickeloxide layers formed according to embodiments of the present invention;

FIG. 8 is a graph illustrating a forming voltage vs. thicknesscharacteristic of various transition metal oxide layers formed accordingto embodiments of the present invention;

FIG. 9 is a graph illustrating a switching characteristic of a nickeloxide layer formed according to an embodiment of the present invention;and

FIG. 10 is a graph illustrating switching endurance test results ofresistance RAM cells employing nickel oxide layers manufacturedaccording to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown. The invention may, however, be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the concept of the invention to those skilled in the art. In thedrawings, the thicknesses of layers and regions are exaggerated forclarity. Like reference numerals in the drawings denote like elements.

FIG. 1 is a cross-sectional view illustrating a pair of non-volatilememory cells, e.g., a pair of resistance RAM cells according toembodiments of present invention. Referring to FIG. 1, an isolationlayer 3 is provided at a predetermined region of a semiconductorsubstrate 1 to define an active region. First and second drain regions 9d′ and 9 d″, which are spaced apart from each other, are provided in theactive region. A common source region 9 s is provided in the activeregion between the first and second drain regions 9 d′ and 9 d″. A firstgate electrode 7 a is disposed to cross over the active region betweenthe common source region 9 s and the first drain region 9 d′, and asecond gate electrode 7 b is disposed to cross over the active regionbetween the common source region 9 s and the second drain region 9 d″.The first and second gate electrodes 7 a and 7 b extend to act as firstand second word lines, respectively. The first and second gateelectrodes 7 a and 7 b are insulated from the active region by a gateinsulating layer 5. The first word line 7 a, the common source region 9s and the first drain region 9 d′ constitute a first access transistor,and the second word line 7 b, the common source region 9 s and thesecond drain region 9 d″ constitute a second access transistor.

The access transistors and the isolation layer 3 are covered with aninsulating layer 20. The insulating layer 20 may be a silicon oxidelayer, a silicon nitride layer or a combination layer thereof. Thecommon source region 9 s is electrically connected to a common sourceline 17 s in the insulating layer 20 through a source contact plug 13 s.The common source line 17 s may be disposed to be parallel with the wordlines 7 a and 7 b. The first drain region 9 d′ is electrically connectedto a first node contact plug 22 d′ that penetrates the insulating layer20, and the second drain region 9 d″ is electrically connected to asecond node contact plug 22 d″ that penetrates the insulating layer 20.

First and second data storage elements 30 a and 30 b are provided on theinsulating layer 20. The first data storage element 30 a is disposed tocover the first node contact plug 22 d′, and the second data storageelement 30 b is disposed to cover the second node contact plug 22 d″.Each of the first and second data storage elements 30 a and 30 b mayinclude a lower electrode 25, a transition metal oxide layer pattern 27and an upper electrode 29, which are sequentially stacked.

The lower electrode 25 is preferably an oxidation resistant metal layer.For example, the lower electrode 25 may be an iridium (Ir) layer, aplatinum (Pt) layer, an iridium oxide (IrO) layer, a titanium nitride(TiN) layer, a titanium aluminum nitride (TiAlN) layer, a ruthenium (Ru)layer or a ruthenium oxide (RuO) layer. Alternatively, the lowerelectrode 25 may be a polysilicon layer.

The transition metal oxide layer pattern 27 can be represented by achemical formula M_(x)O_(y). In the chemical formula, the characters“M”, “O”, “x” and “y” indicate transition metal, oxygen, a transitionmetal composition and an oxygen composition, respectively. In theseembodiments, the oxygen composition “y” of the transition metal oxidelayer pattern 27 is preferably less than it would be in a stable stateof the transition metal oxide layer pattern 27. In other words, it ispreferable that the transition metal oxide layer pattern 27 hasexcessive transition metal content in comparison to a stable transitionmetal oxide layer pattern. This is because a switching characteristic(for example, a switching voltage such as a reset voltage and a setvoltage) of the transition metal oxide layer pattern 27 may be improvedwhen the transition metal content in the transition metal oxide layerpattern 27 is excessive.

In an embodiment of the present invention, if the transition metal “M”is nickel (Ni), cobalt (Co), zinc (Zn) or copper (Cu), the transitionmetal oxide layer pattern 27 has a stable state when both of thetransition metal composition “x” and the oxygen composition “y” are 1.In this case, in order to improve the switching characteristic of thetransition metal oxide layer pattern 27, e.g., a nickel oxide(Ni_(x)O_(y)) layer, a cobalt oxide (Co_(x)O_(y)) layer, a zinc oxide(Zn_(x)O_(y)) layer or a copper oxide (Cu_(x)O_(y)) layer, the oxygencomposition “y” is preferably less than 1 when the composition “x” ofthe nickel (Ni), the cobalt (Co), the zinc (Zn) or the copper (Cu) is 1.More preferably, the oxygen composition “y” is within a range of 0.5 to0.99 when the composition “x” of the nickel (Ni), the cobalt (Co), thezinc (Zn) or the copper (Cu) is 1.

In another embodiment, if the transition metal “M” is hafnium (Hf),zirconium (Zr), titanium (Ti) or chromium (Cr), the transition metaloxide layer pattern 27 has a stable state when the transition metalcomposition “x” and the oxygen composition “y” are 1 and 2,respectively. In this case, in order to improve the switchingcharacteristic of the transition metal oxide layer pattern 27, e.g., ahafnium oxide (Hf_(x)O_(y)) layer, a zirconium oxide (Zr_(x)O_(y))layer, a titanium oxide (Ti_(x)O_(y)) layer or a chromium oxide(Cr_(x)O_(y)) layer, the oxygen composition “y” is preferably less than2 when the composition “x” of the hafnium (Hf), the zirconium (Zr), thetitanium (Ti) or the chromium (Cr) is 1. More preferably, the oxygencomposition “y” is within a range of 1 to 1.98 when the composition “x”of the hafnium (Hf), the zirconium (Zr), the titanium (Ti) or thechromium (Cr) is 1.

In still another embodiment, if the transition metal “M” is iron (Fe),the transition metal oxide layer pattern 27 has a stable state when thetransition metal composition “x” and the oxygen composition “y” are 2and 3 respectively. In this case, in order to improve the switchingcharacteristic of the transition metal oxide layer pattern 27, e.g., aniron oxide (Fe_(x)O_(y)) layer, the oxygen composition “y” is preferablyless than 3 when the composition “x” of the iron (Fe) is 2. Morepreferably, the oxygen composition “y” is within a range of 1.5 to 2.97when the composition “x” of the iron (Fe) is 2.

In yet still another embodiment, if the transition metal “M” is niobium(Nb), the transition metal oxide layer pattern 27 has a stable statewhen the transition metal composition “x” and the oxygen composition “y”are 2 and 5 respectively. In this case, in order to improve theswitching characteristic of the transition metal oxide layer pattern 27,e.g., a niobium oxide (Nb_(x)O_(y)) layer, the oxygen composition “y” ispreferably less than 5 when the composition “x” of the niobium (Nb) is2. More preferably, the oxygen composition “y” is within a range of 2.5to 4.95 when the composition “x” of the niobium (Nb) is 2. Moreover, thetransition metal oxide layer pattern 27 may be a combination of thetransition metal oxide layer patterns having the aforementionedexcessive transition metal content (i.e., a composite of multipletransition metal oxide layers). In addition, the transition metal oxidelayer pattern 27 may contain impurity ions such as lithium (Li) ions,calcium (Ca) ions, chromium (Cr) ions or Lanthanum (La) ions.

The upper electrode 29 may also be an oxidation resistant metal layer.For example, the upper electrode 29 may be an iridium (Ir) layer, aplatinum (Pt) layer, an iridium oxide (IrO) layer, a titanium nitride(TiN) layer, a titanium aluminum nitride (TiAlN) layer, a ruthenium (Ru)layer or a ruthenium oxide (RuO) layer. Alternatively, the upperelectrode 29 may be a polysilicon layer.

Buffer layer patterns 23 may be interposed between the data storageelements 30 a and 30 b and the insulating layer 20. The buffer layerpatterns 23 may extend to cover the node contact plugs 22 d′ and 22 d″.The buffer layer patterns 23 serve as a wetting layer that improvesadhesion between the lower electrodes 25 and the insulating layer 20.Each of the buffer layer patterns 23 may be a single buffer layer. Thesingle buffer layer may be a titanium (Ti) layer, a titanium nitride(TiN) layer, a titanium aluminum nitride (TiAlN) layer, a tantalum (Ta)layer or a tantalum nitride (TaN) layer. Alternatively, each of thebuffer layer patterns 23 may comprise a lower buffer layer pattern andan upper buffer layer pattern, which are sequentially stacked. In thiscase, the lower buffer layer pattern may be one of a titanium (Ti)layer, a titanium nitride (TiN) layer, a titanium aluminum nitride(TiAlN) layer, a tantalum (Ta) layer and a tantalum nitride (TaN) layer,and the upper buffer layer pattern may also be one of a titanium (Ti)layer, a titanium nitride (TiN) layer, a titanium aluminum nitride(TiAlN) layer, a tantalum (Ta) layer and a tantalum nitride (TaN) layer.

The data storage elements 30 a and 30 b and the insulating layer 20 maybe covered with an inter-metal dielectric layer 33. The inter-metaldielectric layer 33 may be a silicon oxide layer. In this case, adhesionbetween the inter-metal dielectric layer 33 and the electrodes 25 and 29may be weak. In addition, the silicon oxide layer used as theinter-metal dielectric layer 33 may exhibit a parasitic switchingcharacteristic, even though weaker than that of the transition metaloxide layer pattern 27. Moreover, in the event that sidewalls of thetransition metal oxide layer patterns 27 are in direct contact with theinter-metal dielectric layer 33, impurities such as silicon atoms in theinter-metal dielectric layer 33 may be diffused into the transitionmetal oxide layer patterns 27 to degrade the switching characteristic ofthe transition metal oxide layer patterns 27. Therefore, in order toimprove adhesion between the inter-metal dielectric layer 33 and theelectrodes 25 and 29 and prevent the switching characteristic of thetransition metal oxide layer patterns 27 from being degraded, a cappinglayer 31 may be provided between the data storage elements 30 a and 30 band the inter-metal dielectric layer 33. The capping layer 31 may extendto cover the insulating layer 20. In the event that the buffer layerpatterns 23 are provided, the capping layer 31 may cover the sidewallsof the buffer layer patterns 23. The capping layer 31 may be an aluminumoxide (AlO) layer.

A bit line 37 may be disposed on the inter-metal dielectric layer 33.The bit line 37 may be electrically connected to the upper electrodes 29through bit line contact plugs 35 a and 35 b that penetrate theinter-metal dielectric layer 33 and the capping layer 31. The bit line37 may be disposed to cross over the word lines 7 a and 7 b. The firstdata storage element 30 a and the first access transistor constitutes afirst resistance RAM cell, and the second data storage element 30 b andthe second access transistor constitutes a second resistance RAM cell.

Now, methods of driving the resistance RAM cells according to the aboveembodiments will be described in brief. First, in order to selectivelystore a desired data in any one (for example, the first resistance RAMcell) of the resistance RAM cells, the common source line 17 s isgrounded and the first access transistor is selectively turned on. Inorder to selectively turn on the first access transistor, a word linevoltage, which is higher than a threshold voltage of the first accesstransistor, is applied to the first word line 7 a. In this case, thesecond word line 7 b is grounded to turn off the second accesstransistor. Next, a reset voltage or a set voltage is applied to the bitline 37 while the first access transistor is turned on. In general, theset voltage is higher than the reset voltage.

When the set voltage is applied to the bit line 37, a conductivefilament is formed in the transition metal oxide layer pattern 27 of thefirst data storage element 30 a to reduce the electrical resistance ofthe first data storage element 30 a. On the contrary, when the resetvoltage is applied to the bit line 37, the conductive filament in thefirst data storage element 30 a is removed to increase the electricalresistance of the first data storage element 30 a.

The initial transition metal oxide layer pattern 27 may exhibit highelectrical resistance that corresponds to a reset state that does nothave the conductive filament. In this case, even though the set voltageis applied to the initial transition metal oxide layer pattern 27, theconductive filament may not be formed in the initial transition metaloxide layer pattern 27. This may be due to a poor interfacecharacteristic between the initial transition metal oxide layer pattern27 and the electrodes 25 and 29 and/or a material property of theinitial transition metal oxide layer pattern 27. Therefore, in order tocompletely convert the initial transition metal oxide layer pattern 27to a conductor exhibiting a normal set state, it may be necessary toapply a forming voltage higher than the set voltage to the transitionmetal oxide layer pattern 27. The switching characteristic of thetransition metal oxide layer pattern 27 may have direct influence on thematerial property of the transition metal oxide layer pattern 27. Inother words, the set voltage, the reset voltage and the forming voltagemay be determined according to the composition ratio and the thicknessof the transition metal oxide layer pattern 27.

Next, an operation of reading the data stored in the first resistanceRAM cell may be achieved by applying a ground voltage, a word linevoltage and a read voltage to the common source line 17 s, the firstword line 7 a and the bit line 37 respectively. The applied read voltageshould be lower than the reset voltage in order to prevent the firstresistance RAM cell from being programmed during the read operation. Inthe event that the transition metal oxide layer pattern 27 of the firstdata storage element 30 a has the set state (low resistance), a largeset current flows through the bit line 37, the first data storageelement 30 a and the first access transistor. As a result, the appliedread voltage applied to the bit line 37 falls down to a first readvoltage which is lower than the applied read voltage. On the other hand,in the event that the transition metal oxide layer pattern 27 of thefirst data storage element 30 a has the reset state (high resistance), asmall reset current flows through the bit line 37, the first datastorage element 30 a and the first access transistor. As a result, theread voltage applied to the bit line 37 rises up to a second readvoltage, which is higher than the applied read voltage. Accordingly, asense amplifier (not shown) connected to the bit line 37 candiscriminate whether the data stored in the selected resistance RAM cellis a logic “1” or a logic “0” using a reference voltage between thefirst and second read voltages.

FIGS. 2 to 4 are cross-sectional views to illustrate methods ofmanufacturing the resistance RAM cells shown in FIG. 1. Referring toFIG. 2, an isolation layer 3 is formed at a predetermined region of asemiconductor substrate 1 to define an active region. A gate insulatinglayer 5 is formed on the active region, and a gate conductive layer isformed on the substrate having the gate insulating layer 5. The gateconductive layer is patterned to form a pair of gate electrodes, forexample, first and second gate electrodes 7 a and 7 b that crosses overthe active region. The first and second gate electrodes 7 a and 7 b mayextend to serve as first and second word lines respectively.

Impurity ions are implanted into the active region using the word lines7 a and 7 b as ion implantation masks, thereby forming a common sourceregion 9 s as well as first and second drain regions 9 d′ and 9 d″. Thecommon source region 9 s is formed in the active region between the wordlines 7 a and 7 b. In addition, the first drain region 9 d′ is formed inthe active region which is adjacent to the first word line 7 a andlocated opposite the common source region 9 s, and the second drainregion 9 d″ is formed in the active region which is adjacent to thesecond word line 7 b and located opposite the common source region 9 s.The first word line 7 a, the common source region 9 s and the firstdrain region 9 d′ constitute a first access transistor TA1, and thesecond word line 7 b, the common source region 9 s and the second drainregion 9 d″ constitute a second access transistor TA2. A firstinterlayer insulating layer 11 is formed on the substrate having thefirst and second access transistors TA1 and TA2. The first interlayerinsulating layer 11 may be formed of a silicon oxide layer.

Referring to FIG. 3, the first interlayer insulating layer 11 ispatterned to form first and second drain contact holes exposing thefirst and second drain regions 9 d′ and 9 d″ as well as a common sourcecontact hole exposing the common source region 9 s. A conductive layersuch as a doped polysilicon layer is formed on the substrate having thedrain contact holes and the common source contact hole, and theconductive layer is planarized to expose an upper surface of the firstinterlayer insulating layer 11. As a result, first and second draincontact plugs 13 d′ and 13 d″ are formed in the first and second draincontact holes respectively, and a common source contact plug 13 s isformed in the common source contact hole.

A conductive layer such as a metal layer is formed on the substratehaving the contact plugs 13 d′, 13 d″ and 13 s. The conductive layer isthen patterned to form a common source line 17 s covering the commonsource contact plug 13 s as well as first and second drain pads 17 d′and 17 d″ respectively covering the first and second drain contact plugs13 d′ and 13 d″. The common source line 17 s may be formed to beparallel to the word lines 7 a and 7 b. Then, a second interlayerinsulating layer 19 is formed on the substrate having the drain pads 17d′ and 17 d″ as well as the common source line 17 s. The secondinterlayer insulating layer 19 may be formed of an insulating layer suchas a silicon oxide layer. The first and second interlayer insulatinglayers 11 and 19 constitute a composite insulating layer 20.

First and second node contact plugs 21 d′ and 21 d″ may be formed in thesecond interlayer insulating layer 19. The first and second node contactplugs 21 d′ and 21 d″ are formed to be in contact with the fist andsecond drain pads 17 d′ and 17 d″, respectively. The node contact plugs21 d′ and 21 d″ are formed of a conductive layer. A lower electrodelayer is then formed on the substrate having the node contact plugs 21d′ and 21 d″. The lower electrode layer is preferably formed of anoxidation resistant metal layer. This is because the interfacecharacteristic between the lower electrode layer and a material layercontacting the lower electrode may be degraded if the lower electrodelayer is oxidized during a subsequent thermal process. In theembodiments of the present invention, the lower electrode layer may beformed of an iridium (Ir) layer, a platinum (Pt) layer, an iridium oxide(IrO) layer, a titanium nitride (TiN) layer, a titanium aluminum nitride(TiAlN) layer, a ruthenium (Ru) layer or a ruthenium oxide (RuO) layer.Alternatively, the lower electrode layer may be formed of a polysiliconlayer.

A conductive buffer layer may be additionally formed prior to formationof the lower electrode layer. The conductive buffer layer is formed inorder to improve adhesion between the lower electrode layer and thesecond interlayer insulating layer 19. The buffer layer may be formed ofa single buffer layer. In this case, the single buffer layer may beformed of a titanium (Ti) layer, a titanium nitride (TiN) layer, atitanium aluminum nitride (TiAlN) layer, a tantalum (Ta) layer or atantalum nitride (TaN) layer. Alternatively, the buffer layer may beformed by sequentially stacking a lower buffer layer and an upper bufferlayer. In this case, the lower buffer layer may be formed of a titanium(Ti) layer, a titanium nitride (TiN) layer, a titanium aluminum nitride(TiAlN) layer, a tantalum (Ta) layer or a tantalum nitride (TaN) layer.The upper buffer layer may be also formed of a titanium (Ti) layer, atitanium nitride (TiN) layer, a titanium aluminum nitride (TiAlN) layer,a tantalum (Ta) layer or a tantalum nitride (TaN) layer.

A transition metal oxide layer represented by a chemical formulaM_(x)O_(y) is formed on the lower electrode layer. In the chemicalformula, the characters “M”, “O”, “x” and “y” indicate transition metal,oxygen, a transition metal composition and an oxygen composition,respectively. In these embodiments, the transition metal oxide layerpreferably has excessive transition metal content in comparison tonormal transition metal content of the transition metal oxide layer at astable state. In other words, the transition oxide layer is preferablyformed to have less oxygen content than the transition metal oxide layerhaving a stable state. This is because the switching characteristic (forexample, switching voltages such as a reset voltage and a set voltage)of the transition metal oxide layer may be improved when the transitionmetal content is excessive.

In an embodiment of the present invention, the transition metal oxidelayer may be formed of a nickel oxide (Ni_(x)O_(y)) layer, a cobaltoxide (Co_(x)O_(y)) layer, a zinc oxide (Zn_(x)O_(y)) layer or a copperoxide (Cu_(x)O_(y)) layer. In this case, it is preferable that thetransition metal oxide layer is formed so that the oxygen composition“y” is within a range of 0.5 to 0.99 when the composition “x” of thenickel (Ni), the cobalt (Co), the zinc (Zn) or the copper (Cu) is 1. Inanother embodiment, the transition metal oxide layer may be formed of ahafnium oxide (Hf_(x)O_(y)) layer, a zirconium oxide (Zr_(x)O_(y))layer, a titanium oxide (Ti_(x)O_(y)) layer or a chromium oxide(Cr_(x)O_(y)) layer. In this case, it is preferable that the transitionmetal oxide layer is formed so that the oxygen composition “y” is withina range of 1 to 1.98 when the composition “x” of the hafnium (Hf),zirconium (Zr), titanium (Ti) or chromium (Cr) is 1. In still anotherembodiment, the transition metal oxide layer may be formed of an ironoxide (Fe_(x)O_(y)) layer. In this case, it is preferable that thetransition metal oxide layer is formed so that the oxygen composition“y” is within a range of 1.5 to 2.97 when the composition “x” of theiron (Fe) is 2. In yet still another embodiment, the transition metaloxide layer may be formed of a niobium oxide (Nb_(x)O_(y)) layer. Inthis case, it is preferable that the transition metal oxide layer isformed so that the oxygen composition “y” is within a range of 2.5 to4.95 when the composition “x” of the niobium (Nb) is 2. Moreover, thetransition metal oxide layer may be formed as a composite of thetransition metal oxide layers having the aforementioned excessivetransition metal content.

FIG. 5 is a process flowchart that illustrates methods of formingtransition metal oxide layers according to embodiments of the presentinvention. Referring to FIG. 5, a substrate having the lower electrodelayer is loaded into a process chamber, and a transition metal layer maybe formed to a thickness of 5 to 20 Å on the lower electrode layer (step51). The transition metal layer may be formed of a nickel (Ni) layer, acobalt (Co) layer, a zinc (Zn) layer, a copper (Cu) layer, a hafnium(Hf) layer, a zirconium (Zr) layer, a titanium (Ti) layer, a chromium(Cr) layer, an iron (Fe) layer or a niobium (Nb) layer using asputtering technique. The transition metal layer is then oxidized usingan oxygen plasma treatment technique (step 53). The oxygen plasmatreatment process may be performed using an in-situ process without avacuum break. The oxygen composition of the oxidized transition metallayer may be changed according to a process condition of the oxygenplasma treatment process. For example, the oxygen composition of theoxidized transition metal layer may be determined depending on an oxygenplasma treatment time, a flow rate of oxygen and/or a power forgenerating oxygen plasma. Subsequently, the formation process of thetransition metal layer (step 51) and the oxygen plasma treatment process(Step 53) are alternately and repeatedly performed until a cumulativethickness T_(tot) of the oxidized transition metal layers is equal to orgreater than a desired thickness T_(s) (step 55). Alternatively, thetransition metal oxide layer may be formed using an O₂ reactivesputtering technique, a chemical vapor deposition technique or an atomiclayer deposition technique.

Referring again to FIG. 3, an upper electrode layer is formed on thetransition metal oxide layer. The upper electrode layer is preferablyformed of an oxidation resistant metal layer. This is because theinterface characteristic of the lower electrode layer and the transitionmetal oxide layer may be degraded when the upper electrode layer isoxidized during a subsequent thermal process. In these embodiments, theupper electrode layer may be formed of an iridium (Ir) layer, a platinum(Pt) layer, an iridium oxide (IrO) layer, a titanium nitride (TiN)layer, a titanium aluminum nitride (TiAlN) layer, a ruthenium (Ru) layeror a ruthenium oxide (RuO) layer. Alternatively, the upper electrodelayer may be formed of a polysilicon layer.

A hard mask layer may be formed on the upper electrode layer. The hardmask layer may be formed of a material layer having an etchingselectivity with respect to the upper electrode layer, the transitionmetal oxide layer, the lower electrode layer and the buffer layer. Forexample, the hard mask layer may be formed of a silicon nitride (SiN)layer or a titanium nitride (TiN) layer. The hard mask layer ispatterned using a photolithography/etch process, thereby forming hardmask patterns HM on the drain pads 17 d′ and 17 d″. The upper electrodelayer, the transition metal oxide layer, the lower electrode layer andthe buffer layer are then etched in sequence using the hard maskpatterns HM as etching masks. As a result, first and second data storageelements 30 a and 30 b are formed on the first and second node contactplugs 21 d′ and 21 d″ respectively, and buffer layer patterns 23 areformed between the data storage elements 30 a and 30 b and the secondinterlayer insulating layer 19. As shown in FIG. 3, each of the datastorage elements 30 a and 30 b is formed to include a lower electrode25, a transition metal oxide layer pattern 27 and an upper electrode 29which are sequentially stacked. The hard mask patterns HM may be removedafter formation of the data storage elements 30 a and 30 b.

Referring now to FIG. 4, an inter-metal dielectric layer 33 is formed onthe substrate having the data storage elements 30 a and 30 b. Theinter-metal dielectric layer 33 may be formed of a silicon oxide layer.A capping layer 31 may be formed to cover the data storage elements 30 aand 30 b prior to formation of the inter-metal dielectric layer 33. Thecapping layer 31 is formed in order to prevent impurities (for example,silicon atoms) of the inter-metal dielectric layer 33 from beingdiffused into the transition metal oxide layer pattern 27 and improveadhesion between the inter-metal dielectric layer 33 and the electrodes25 and 29. In these embodiments, the capping layer 31 may be formed ofan aluminum oxide (AlO) layer.

The inter-metal dielectric layer 33 and the capping layer 31 arepatterned to form bit line contact holes that expose the upperelectrodes 29, and bit line contact plugs 35 a and 35 b are formed inthe bit line contact holes. A conductive layer such as a metal layer isformed on the substrate having the bit line contact plugs 35 a and 35 b,and the conductive layer is patterned to form a bit line 37 covering thebit line contact plugs 35 a and 35 b. The bit line 37 may be formed tocross over the word lines 7 a and 7 b.

FIG. 6 is a graph illustrating x-ray photo electron spectroscopy (XPS)measurement data in order to obtain composition ratios of nickel oxide(Ni_(x)O_(y)) layers manufactured according to embodiments of thepresent invention. In FIG. 6, the abscissa indicates binding energyE_(B) of elements in the nickel oxide (NiO) layers, and the ordinateindicates the number of photo electrons emitted from the nickel oxide(NiO) layers during a unit time (1 second) when x-rays are irradiatedonto the nickel oxide (NiO) layers. The nickel oxide (NiO) layers wereformed by alternately and repeatedly performing a first process forforming a nickel (Ni) layer using a sputtering technique and a secondprocess for oxidizing the nickel (Ni) layer using an oxygen plasmatreatment technique during a predetermined time Tp. Each of the nickel(Ni) layers was formed to a thickness of 10 Å. The oxygen plasmatreatment process was performed using an RF power of 20 watts and anoxygen gas introduced with a flow rate of 2 sccm (standard cubiccentimeter per minute). In addition, the nickel oxide (NiO) layers wereformed to have a final thickness of 400 Å. Prior to measurement of theXPS data, an argon ion sputter etching process was carried out in orderto remove impurities existing on the surfaces of the nickel oxide (NiO)layers. The argon ion sputter etching process was performed using avoltage of 2 kV for two minutes.

In the graph of FIG. 6, a curve 101 corresponds to measurement resultsof the nickel oxide (NiO) layer formed with the oxygen plasma treatmenttime Tp of 5 seconds, and a curve 102 corresponds to measurement resultsof the nickel oxide (NiO) layer formed with the oxygen plasma treatmenttime Tp of 20 seconds. In addition, a curve 103 corresponds tomeasurement results of the nickel oxide (NiO) layer formed with theoxygen plasma treatment time Tp of 40 seconds, and a curve 104corresponds to measurement results of the nickel oxide (NiO) layerformed with the oxygen plasma treatment time Tp of 120 seconds.

The oxygen compositions “y” of the nickel oxide (Ni_(x)O_(y)) layers,which are calculated from the measurement results of FIG. 6, are listedin the following Table 1.

TABLE 1 Oxygen Plasma Oxygen Composition “y” XPS Data Treatment Time(Tp) (when “x” = 1) Curve 101  5 seconds 0.66 Curve 102 20 seconds 0.77Curve 103 40 seconds 0.84 Curve 104 120 seconds  0.95As can be seen in Table 1, the more the oxygen plasma treatment time Tpwas increased, the more the oxygen composition “y” was also increased.

FIG. 7 is a graph illustrating electrical characteristics of datastorage elements employing nickel oxide (Ni_(x)O_(y)) layersmanufactured according to embodiments of the present invention. In FIG.7, the abscissa indicates the oxygen plasma treatment time Tp describedwith reference to FIG. 6, the left ordinate indicates resistivity ρ ofthe nickel oxide (Ni_(x)O_(y)) layers, and the right ordinate indicatesa forming voltage V_(F) of the data storage elements. The data storageelements were formed to have a rectangular shape having an area of0.3×0.7 μm² when viewed from a plan view, and lower and upper electrodesof the data storage elements were formed of an iridium (Ir) layer havinga thickness of 500 Å. The nickel oxide (Ni_(x)O_(y)) layer interposedbetween the lower and upper electrodes was formed to have a finalthickness of 200 Å. In addition, the nickel oxide (Ni_(x)O_(y)) layerwas formed by alternately and repeatedly performing a process forforming a nickel (Ni) layer using a sputtering technique and a processfor oxidizing the nickel (Ni) layer using an oxygen plasma treatmenttechnique, as described with reference to FIG. 6. That is, the nickel(Ni) layer was formed to a thickness of 10 Å, and the oxygen plasmatreatment process was performed using an RF power of 20 watts and anoxygen gas injected with a flow rate of 2 sccm.

Referring to FIG. 7, the more the oxygen plasma treatment time Tp wasincreased, the more the resistivity ρ of the nickel oxide (NiO) layerwas also increased. When the oxygen plasma treatment process wasperformed for about 3 to 200 seconds, the data storage elementsexhibited a low forming voltage V_(F) of about 1.5 V to 8 V.

In the meantime, when the oxygen plasma treatment process was performedfor about 5 to 120 seconds, the nickel oxide (Ni_(x)O_(y)) layersexhibited the switching characteristics. As can be seen in Table 1 andFIG. 7, the nickel oxide (Ni_(x)O_(y)) layer exhibited the oxygencomposition “y” of about 0.66 and the resistivity ρ of about 0.01 Ω·cmwhen the oxygen plasma treatment process was performed for 5 seconds,and the nickel oxide (Ni_(x)O_(y)) layer exhibited the oxygencomposition “y” of about 0.95 and the resistivity ρ of about 100 Ω·cmwhen the oxygen plasma treatment process was performed for 120 seconds.

FIG. 8 is a graph illustrating forming voltages of data storage elementsthat employ various transition metal oxide layers manufactured accordingto embodiments of the present invention. In FIG. 8, the abscissaindicates a thickness T of the transition metal oxide layers, and theordinate indicates the forming voltage V_(F) of the transition metaloxide layers. The lower and upper electrodes of the data storageelements were formed of an iridium (Ir) layer having a thickness of 500Å. In addition, the data storage elements were formed to have arectangular shape having an area of 0.3×0.7 μm² when viewed from a planview.

In the graph of FIG. 8, when the transition metal oxide layers wereformed of a nickel oxide (Ni_(x)O_(y)) layer, the nickel oxide(Ni_(x)O_(y)) layers were fabricated by applying the oxygen plasmatreatment time Tp of 20 seconds. In other words, the nickel oxide(Ni_(x)O_(y)) layers were formed to have the oxygen composition “y” of0.77 with the nickel composition “x” of 1. In the event that thetransition metal oxide layers were formed of hafnium oxide (Hf_(x)O_(y))layers or zirconium oxide (Zr_(x)O_(y)) layers, the hafnium oxide(Hf_(x)O_(y)) layers or the zirconium oxide (Zr_(x)O_(y)) layers werealso formed using the sputtering technique and the oxygen plasmatreatment technique. In other words, the hafnium oxide (Hf_(x)O_(y))layers and the zirconium oxide (Zr_(x)O_(y)) layers were formed byalternately and repeatedly performing the sputtering process and theoxygen plasma treatment process.

In the meantime, when the transition metal oxide layers were formed oftitanium oxide (Ti_(x)O_(y)) layers, an O₂ reactive sputtering techniquewas used to form the titanium oxide (Ti_(x)O_(y)) layers. In this case,the O₂ reactive sputtering process was performed at a temperature of350° C. with a power of 10 kW. As can be seen in the graph of FIG. 8,the nickel oxide (Ni_(x)O_(y)) layers among the various transition metaloxide layers exhibited the lowest forming voltage. In particular, whenthe titanium oxide (Ti_(x)O_(y)) layers were formed to have a thicknessof 200 Å, the titanium oxide (Ti_(x)O_(y)) layers exhibited a lowforming voltage of about 2.5 V.

FIG. 9 is a graph illustrating a switching characteristic (I-V curve) ofa data storage element that employs a nickel oxide layer manufacturedaccording to an embodiment of the present invention. In FIG. 9, theabscissa indicates a voltage V_(A) between the upper and lowerelectrodes of the data storage element, and the ordinate indicates acurrent I that flows through the nickel oxide (Ni_(x)O_(y)) layer. Thelower and upper electrodes of the data storage element were formed of aniridium (Ir) layer having a thickness of 500 Å, and the nickel oxide(Ni_(x)O_(y)) layer was formed to have a final thickness of 200 Å. Inaddition, the nickel oxide (Ni_(x)O_(y)) layer was formed by alternatelyand repeatedly performing a first process for forming a nickel (Ni)layer using a sputtering technique and a second process for oxidizingthe nickel (Ni) layer using an oxygen plasma treatment technique. Thesecond process, that is, the oxygen plasma treatment process, wasperformed using an RF power of 20 watts and an oxygen gas injected witha flow rate of 2 sccm for 20 seconds. In addition, the data storageelements were formed to have a rectangular shape having an area of0.3×0.7 μm² when viewed from a plan view.

Referring to FIG. 9, when the voltage V_(A) between the upper and lowerelectrodes was about 0.5 V, the nickel oxide (Ni_(x)O_(y)) layer wasswitched to a reset state having a high resistance. On the other hand,when the voltage V_(A) between the upper and lower electrodes was about1.1 V, the nickel oxide (Ni_(x)O_(y)) layer was switched to a set statehaving a low resistance. A maximum allowable current (currentcompliance) was set to about 0.5 mA during application of the voltageV_(A) in order to convert the nickel oxide (Ni_(x)O_(y)) layer to theset state. This limit is applied to prevent the nickel oxide(Ni_(x)O_(y)) layer from being damaged when a large amount of currentflows through the nickel oxide (Ni_(x)O_(y)) layer having the set state.As shown in FIG. 9, the characteristic curve of the titanium oxide(Ti_(x)O_(y)) layer manufactured according to embodiments of the presentinvention was substantially symmetrical with respect to the cross pointof the abscissa and the ordinate (point having coordinate of 0 V and 0mA).

FIG. 10 is a graph illustrating switching endurance test results to datastorage elements having nickel oxide layers manufactured according toembodiments of the present invention. The data storage elements weremanufactured using the same method as described with reference to FIG.9. In FIG. 10, the abscissa indicates the number N of switchingoperations, that is, the number of program cycles, and the ordinateindicates an electrical resistance R of the data storage elements. Areset voltage of 0.8 V was applied to the nickel oxide layers throughthe upper and lower electrodes for 1 millisecond in order to switch thedata storage elements to the reset state. In addition, a set voltage of1.5 V was applied to the nickel oxide layers through the upper and lowerelectrodes for 1 millisecond in order to switch the data storageelements to the set state. A maximum allowable current of about 0.5 mAwas set while the set voltage was applied. As can be seen in FIG. 10,even though the data storage elements were subject to 1×10¹⁶ repetitionsof the reset and set operations, the data storage elements exhibited aset resistance Rs lower than about 1,000 Ω and a reset resistance Rrhigher than about 10,000Ω. According to the present invention asdescribed above, it is possible to reduce operation voltages of anon-volatile memory cell employing a transition metal oxide layer byadjusting a composition ratio of the transition metal oxide layer.Therefore, it is possible to easily realize a high performanceresistance RAM device.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A memory cell, comprising: a memory element having a M_(x)O_(y)region therein that supports non-volatile data storage, where M is atransition metal, O is oxygen, “x” and “y” are positive real numbers andx/y is greater than a same ratio associated with a stabilized transitionmetal oxide having the same transition metal.
 2. The memory cell ofclaim 1, wherein “x” equals 1.0, “y” is in the range from 0.5 to 0.99and M is selected from a group consisting of nickel (Ni), cobalt (Co),zinc (Zn) and copper (Cu).
 3. The memory cell of claim 1, wherein “x”equals 1.0, “y” is in the range from 1.0 to 1.98 and M is selected froma group consisting of hafnium (Hf), zirconium (Zr), titanium (Ti) andchromium (Cr).
 4. The memory cell of claim 1, wherein “x” equals 2.0,“y” is in the range from 1.5 to 2.97 and M is iron (Fe).
 5. The memorycell of claim 1, wherein “x” equals 2.0, “y” is in the range from 2.5 to4.95 and M is niobium (Nb).
 6. The memory cell of claim 1, furthercomprising at least one electrode contacting the M_(x)O_(y) region, saidat least one electrode comprising a material selected from a groupconsisting of iridium (Ir), platinum (Pt), iridium oxide (IrO), titaniumnitride (TiN), titanium aluminum nitride (TiAIN), ruthenium (Ru),ruthenium oxide (RuO) and polysilicon.
 7. A memory cell, comprising: amemory element having a MO_(0.5≦y≦0.99) region therein that supportsnon-volatile data storage, where O is oxygen and M is a transition metalselected from a group consisting of nickel (Ni), cobalt (Co), zinc (Zn)and copper (Cu).
 8. A non-volatile memory cell, comprising: aninsulating layer formed on a semiconductor substrate; lower and upperelectrodes formed over the insulating layer, the lower and upperelectrodes being overlapped with each other; a transition metal oxidelayer pattern interposed between the lower and upper electrodes, thetransition metal oxide layer pattern being represented by a chemicalformula M_(x)O_(y), wherein the characters “M”, “O”, “x” and “y”indicate transition metal, oxygen, a transitional metal composition andan oxygen composition respectively, and the transition metal oxide layerpattern contains excessive transition metal content in comparison to astabilized transition metal oxide layer pattern.
 9. The non-volatilememory cell according to claim 8, wherein the oxygen composition “y” iswithin a range of 0.5 to 0.99 when the transition metal “M” is nickel(Ni), cobalt (Co), zinc (Zn) or copper (Cu) and the transition metalcomposition “x” is
 1. 10. The non-volatile memory cell according toclaim 8, wherein the oxygen composition “y” is within a range of 1.0 to1.98 when the transition metal “M” is hafnium (Hf), zirconium (Zr),titanium (Ti) or chromium (Cr) and the transition metal composition “x”is
 1. 11. The non-volatile memory cell according to claim 8, wherein theoxygen composition “y” is within a range of 1.5 to 2.97 when thetransition metal “M” is iron (Fe) and the transition metal composition“x” is
 2. 12. The non-volatile memory cell according to claim 8, whereinthe oxygen composition “y” is with a range of 2.5 to 4.95 when thetransition metal “M” is niobium (Nb) and the transition metalcomposition “x” is
 2. 13. The non-volatile memory cell according toclaim 8, wherein the lower electrode is an iridium (Ir) layer, aplatinum (Pt) layer, an iridium oxide (IrO) layer, a titanium nitride(TiN) layer, a titanium aluminum nitride (TiAIN) layer, a ruthenium (Ru)layer, a ruthenium oxide (RuO) layer or a polysilicon layer.
 14. Thenon-volatile memory cell according to claim 8, wherein the upperelectrode is an iridium (Ir) layer, a platinum (Pt) layer, an iridiumoxide (IrO) layer, a titanium nitride (TiN) layer, a titanium aluminumnitride (TiAIN) layer, a ruthenium (Ru) layer, a ruthenium oxide (RuO)layer or a polysilicon layer.
 15. The non-volatile memory cell accordingto claim 8, further comprising a contact plug that penetrates theinsulating layer to electrically connect the lower electrode to thesemiconductor substrate.
 16. The non-volatile memory cell according toclaim 15, further comprising a buffer layer pattern, which is interposedbetween the lower and upper electrodes and extended to cover the contactplug.
 17. The non-volatile memory cell according to claim 16, whereinthe buffer layer pattern comprises a titanium (Ti) layer, a titaniumnitride (TiN) layer, a titanium aluminum nitride (TiAIN) layer, atantalum (Ta) layer or a tantalum nitride (TaN) layer.
 18. Thenon-volatile memory cell according to claim 16, wherein the buffer layerpattern comprises a lower buffer layer pattern and an upper buffer layerpattern, which are sequentially stacked.
 19. The non-volatile memorycell according to claim 18, wherein the lower buffer layer pattern isone of a titanium (Ti) layer, a titanium nitride (TiN) layer, a titaniumaluminum nitride (TiAIN) layer, a tantalum (Ta) layer and a tantalumnitride (TaN) layer, and the upper buffer layer pattern is one of atitanium (Ti) layer, a titanium nitride (TIN) layer, a titanium aluminumnitride (TiAIN) layer, a tantalum (Ta) layer and a tantalum nitride(TaN) layer.
 20. The non-volatile memory cell according to claim 8,further comprising: an inter-metal dielectric layer formed on thesubstrate having the lower electrode, the transition metal oxide layerpattern and the upper electrode; and a bit line formed on theinter-metal dielectric layer and electrically connected to the upperelectrode.
 21. The non-volatile memory cell according to claim 8,further comprising: a capping layer covering the lower electrode, thetransition metal oxide layer pattern and the upper electrode; aninter-metal dielectric layer formed on the capping layer; and a bit lineformed on the inter-metal dielectric layer and electrically connected tothe upper electrode.
 22. The non-volatile memory cell according to claim21, wherein the capping layer is an aluminum oxide (AIO) layer.
 23. Thenon-volatile memory cell according to claim 8, further comprising anaccess transistor formed at the semiconductor substrate, wherein theaccess transistor includes a pair of source/drain regions formed in thesemiconductor substrate and a gate electrode disposed to cross over achannel region between the pair of source/drain regions, and the lowerelectrode is electrically connected to the drain region.